A prosthesis is a device for replacing a missing part of a body, such as a leg or portion thereof. FIGS. 22 and 23 illustrate a prior art prosthetic device known as an "endoskeletal prosthesis". The endoskeletal prosthesis includes an elongated endoskeletal support member tube 202, which is typically an aluminum tube or "pylon". One end of tube 202 is connected to an artificial extremity, such as foot 204, and the other is connected to patient 206 via a stump socket 208.
The term stump refers to the end of a patient's severed limb. A stump socket is worn by a patient around the stump and a portion of the remaining limb. Typically, the stump socket is custom-made to fit a particular patient. The prosthesis is then attached to the stump socket by means of an attachment device which can be an integral part of the stump socket. Examples of such attachment devices are provided by U.S. Pat. No. 5,163,965, issued Nov. 17, 1992, the disclosure of which is hereby incorporated by reference.
When a patient is fitted for an endoskeletal prosthesis, the prosthesis must be properly aligned with the patient's stump socket and artificial foot or hand. The arrows in FIGS. 22 and 23 illustrate directions in which the endoskeletal tube 202 can be aligned with respect to stump socket 208 or foot 204. Medical practitioners generally use the following terminology to refer to these alignment adjustments: plantar and dorsi (illustrated by arrows 210 and 211, respectively, as shown in FIG. 23), inversion and eversion (illustrated by arrows 212 and 213, respectively, as shown in FIG. 22), abduction and adduction (illustrated by arrows 214 and 216, respectively, as shown in FIG. 22) and flexion and extension (illustrated by arrows 218 and 220, respectively, as shown in FIG. 23).
Attachment modules such as module 222 of FIG. 24 are commonly used to provide these alignment adjustments. Module 222 consists of an adapter plate 224 and an sleeve-like adapter 226. Adapter plate 224 is two-sided, and has a first convex side, from which a pyramid-shaped knob 228 extends. A second side 230 of adapter plate 224 is bolted to an attachment device (not shown) at the end of the stump socket. Adapter 226 itself is a hollow cylinder or sleeve. Pyramid-shaped knob 228 is inserted into one end of sleeve-like adapter 226. The other end of adapter 226 is clamped or otherwise mounted to endoskeletal pylon 202.
The plate and adaptor are then coupled using four fitment bolts or set bolts 232, 234, 236 and 238. Bolts 232-238 extend through the walls of adapter 226 and engage pyramid-shaped knob 228 to couple adapter plate 224 to adapter 226, thereby attaching endoskeletal pylon 202 to stump socket 208. By adjusting the fitment bolts, medical personnel can effect the above-described types of alignment adjustments.
When plate 224 and adapter 226 are thus coupled, they are pressed tightly together. It will be noted that top rim 240 of adapter 226 has a concave face which mates with the convex side of plate 224. Thus, no matter at what angle adapter 226 is positioned relative to plate 224, top rim 240 of adapter 226 remains in complete physical contact with the convex surface of plate 224.
Attachment module 222 shown in FIG. 24 is used to attach the upper end of an endoskeletal pylon to a stump socket. A similar arrangement is used to attach the bottom of the endoskeletal pylon to an artificial foot. When used for this purpose, a foot adapter plate 242 (shown in FIGS. 25-27) is used in lieu of stump adapter plate 224. Like adapter plate 224, foot adapter plate 242 has a pyramid-shaped knob 244 which is placed in sleeve-like adapter 226 (not shown in FIGS. 25-27).
While the foregoing prior art arrangement is workable, it has several drawbacks. Specifically, when used to attach an artificial leg, attachment module 222 is subjected to tremendous longitudinal or vertical tension and compression forces when patient 206 walks or runs which adversely affect plate 224 and adapter 226. These forces are transmitted up endoskeletal pylon 202 and to adapter 226, where they are borne by the fitment bolts, which are tightened to impinge on and hold the pyramid-shaped knob.
It will be observed that this longitudinal force is nearly perpendicular to the front faces of fitment bolts 232-238, and therefore the force is transmitted to each bolt as a shearing (as opposed to compressing) force. This shearing is resisted by the friction between the faces of fitment bolts 232-238 and pyramid-shaped knob 228. The shearing force does, however, urge bolts 232-238 to slide along and into knob 228, thereby eventually causing deformation of knob 228 and/or bolts 232-238, particularly for relatively heavy patients, such as those who weigh more than two hundred pounds. Eventually, action of the ends of bolts 232-238 against knob 228 from use of prosthetic device 200 causes significant deformation of pyramid-shaped knob 228. The result is a loosening of the coupling which can be followed by a sudden catastrophic failure of module 222. The patient's artificial leg can literally fall off in mid-stride.
To alleviate this problem, fitment bolts 232-238 in attachment module 222 extend somewhat at an angle from horizontal. This allows some component of longitudinal force to be borne as a compression force by the main body of the fitment bolts. While extending the bolts downwardly improves the performance of module 222, it also makes the fitment bolts more difficult for medical personnel to install and adjust.
Another drawback of module 222 is that reinforcements such as reinforcements 246 must be provided in the wall of sleeve-like adapter 226. These reinforcements are necessary because the fitment bolts which are lodged in the adapter wall must bear the massive longitudinal (vertical) forces discussed above. These reinforcements cause the adapter to be larger than is otherwise necessary. For a variety of reasons, particularly cosmetic, it is desirable to have a more narrow adapter.
Yet another drawback of prior art module 222 is that it uses fitment bolts or bolts having flat (as opposed to rounded) ends. These flat ends are used to improve the friction grip of the bolts. In practice, however, rounded heads provide easier alignment adjustment.